In a microwave-powered lamp, the optical reflector is designed to focus the radiation at a desired point and provide a microwave cavity for efficient coupling of the microwave energy with the bulb. The lamp design is necessarily a compromise between the desired optical characteristics and the required microwave cavity, since designing for certain optical characteristics will also affect the characteristics of the resulting microwave cavity. It is not an easy task to design a reflector that will have both good optical and microwave cavity characteristics. Thus, once a design compromise is reached, it is common to fit the application to the lamp, rather than designing a different lamp for each application. Consequently, prior art lamps have fixed focal points.
If an application requires a different focal point, prior art lamps with fixed focal points are used in a way that may not be most efficient, since the product being cured may not be receiving the optimum energy from the lamp due to mismatch of the lamp's optical characteristics with the actual location of the product in the curing chamber.
There is, therefore, a need for a lamp whose focal point may be adjusted as desired for a specific application without disturbing its basic optical and microwave cavity characteristics.